1. Field of the Invention
This invention relates to automotive turn signals, particularly turn signals used on trucks of the tractor-trailer type. The invention is especially concerned with a control system for returning a manually operated signal selector to a neutral position following a turning maneuver. The process is sometimes referred to as self-cancellation of the turn signal.
2. Description of Prior Developments
Automotive vehicles are commonly equipped with turn signals, i.e. flashing lights on the front and rear ends of a vehicle that warn other motorists that the driver of the vehicle intends to make either a right turn or a left turn. To actuate the turn signal lights, the driver operates a manual lever located on the steering wheel. As the lever is moved from a neutral position to a selected operating position, the associated switches are opened and closed thereby supplying current to flasher devices and the associated turn signal lights.
In many cases, the turn signal system is equipped with a self-cancelling feature which includes a mechanism for automatically returning the manual lever to its neutral position following a turning maneuver By thus returning the lever to its neutral position, the turn signal is cancelled so that the signal lights cease flashing thereby avoiding a false warning to other motorists that the driver might be contemplating another turning maneuver.
The self-cancelling mechanism can include an electrical sensor associated with the vehicle steering wheel to detect whether the steering wheel is in a straight-ahead position or in a turning position. Also, an electrically-operated detent is provided for retaining the lever in its various positions. Springs may be used to bias the lever toward its neutral position.
In operation of the system, when the driver returns the steering wheel to its straight-ahead position following a turning maneuver, the electrical sensor detects the change in steering wheel condition by sending a signal to the electrically-operated detent. The detent releases the lever which allows the associated springs to automatically return the lever to its neutral position. The detent can include an electromagnet coil and a detent structure operated by the coil.
As used in automobiles, the self-cancelling feature is generally effective for its intended purpose. However, when the system is used on trucks of the tractor-trailer type, it may not be satisfactory under all circumstances. For example, while the driver of a tractor-trailer is in the process of making a left turn, he will sometimes swing the truck first to the right and then to the left. The initial right turn provides clearance for the intermediate wheels during the actual left turn. In a similar manner, when making a right turn, the driver will sometimes initially turn the vehicle to the left before making the right turn. Again, this is for the purpose of obtaining sufficient curbside wheel clearance.
When the driver of a tractor-trailer makes two successive turns in opposite directions, as described above, there is a danger that the turn signal system will prematurely self-cancel during the turning process, i.e. before the turn is completed. When this occurs, the following motorist can misinterpret the inadvertent cancellation of the signal as an indication that the driver had decided not to make the turn. Confusion on the part of the following motorist could lead to an accident.
The above-described premature signal cancellation action occurs because the driver moves the steering wheel through the straight-ahead condition during the process of going from one turn direction to the other turn direction. As the steering wheel reaches the straight-ahead condition, the wheel sensor sends a signal to the electromagnetic detent which prematurely returns the signal select lever and associated switches to the neutral, no-turn position.
The present invention is directed to a control system including electrical circuitry for preventing premature cancellation of a turning signal, particularly under the above-described condition wherein the driver sets the signal selector lever in an operating position for a signal and then turns the steering wheel in two different directions during the course of a turning maneuver. In one form of the invention, an electrical timer is interposed between the steering wheel sensor and the electromagnetic detent. When the steering wheel is moved from one turn direction through the straight-ahead position to the other turn direction, the time delay generated by the timer prevents the cancellation signal from reaching the electro-magnetic detent. The timer is designed to terminate or disable the premature cancellation signal.
Electrical timers have previously been employed in turn signal systems. However, such timers have been used primarily for cancelling the turning signal only when the steering wheel is moved an insufficient amount to effect signal cancellation, e.g., when the signal is used to change traffic lanes or when the wheel sensor is ineffective to produce the signal cancellation action.
U.S. Pat. No. 3,308,428 to Grontkowski shows a turn signal system having a timer for cancelling the turn signal at a predetermined time after initial turn-on of the signal lights or after application of foot pressure to the vehicle brake, e.g., when the vehicle is brought to a stop at a traffic light. The timer is apparently used as an override device to effect a signal cancellation action in the event the wheel sensor is ineffective for that purpose.
U.S. Pat. No. 4,792,785 to Yukio, et al. shows a turn signal system having a timer for cancelling a turn signal only when the vehicle is travelling at a high rate of speed. The turn signal is turned off at a predetermined time following initial turnon of the signal lights. The timer is only operative under high speed conditions. Under normal conditions, the steering wheel sensor controls the signal cancellation process.
In both the Grontkowski and Yukio systems, the timer is used as an auxiliary device for turning off the signal, i.e. for signal cancellation. In the present invention, the timer is used as a device for preventing premature cancellation of the signal especially while the steering wheel is passing through a straight-ahead condition from one turn direction to another turn direction.